It is known that precipitated silica has been employed for a long time as a white reinforcing filler in elastomers, in particular in tires.
However, like any reinforcing filler it should be capable of, on the one hand, being handled and, on the other hand and above all, being easily incorporated into mixtures.
It is known, in general, that, to obtain the optimum reinforcing properties imparted by a filler, the latter must be present in the elastomeric matrix in a final form which is at the same time divided as finely as possible and distributed as homogeneously as possible. Now, such conditions can be achieved only insofar as, on the one hand, the filler has a very good capacity for being incorporated into the matrix when mixed with the elastomer (incorporability of the filler) and for being broken up or disintegrated into the form of a very fine powder (disintegration of the filler) and insofar as, on the other hand, the powder resulting from the abovementioned disintegration process can, in its turn, be completely and homogeneously dispersed in the elastomer (dispersion of the powder).
In addition, for mutual affinity reasons, silica particles have an unfortunate tendency to agglomerate together in the elastomer matrix. A detrimental consequence of these silica/silica interactions is that they limit the reinforcing properties to a level which is appreciably lower than that which it would be theoretically possible to reach if all the silica/elastomer interactions capable of being created during the mixing operation were actually obtained (this theoretical number of silica/elastomer interaction being, as is well known, directly proportional to the external surface of the silica employed).
Furthermore, such silica/silica interactions tend, in the raw state, to increase the stiffness and the consistency of the mixtures, thus making them more difficult to process.
The problem which arises is to have available fillers which, while capable of being of a relatively large size, have a very good dispersibility in the elastomers.